1. Field of the Invention
This invention relates to transformers mounted within a case having cooling ducts embedded therein.
2. Description of the Prior Art
The cooling of large transformers has always been a troublesome area for the designer. In the prior art several methods have been used with some success. One method being submerging the transformer core windings in a container containing insulating and cooling oil. However, as the units become larger it was necessary to cool the insulating oil. This was disclosed in U.S. Pat. No. 1,310,097, issued July 15, 1919.
Other methods have been used to cool large transformers such as that disclosed in U.S. Pat. No. 3,371,299 in which there were ducts between the windings which ran to the outside of the transformer. Coolant was circulated through the duct network removing the heat from the transformer and carrying it to the outside atmosphere where the coolant would dissipate the heat. Another method included compartmentalizing the transformer, flowing coolant through the different compartments, and circulating it through a heat exchanger in order to keep the transformer operating within desirable limits. This was disclosed in U.S. Pat. No. 2,685,677 issued Aug. 3, 1954. Also, there have been other methods where windings of the transformer were made with hollow tubing and coolant was forced through the hollow tubing to remove the excess heat. An improvement on using the winding as a coolant conductor was disclosed in U.S. Pat. No. 3,056,071 issued Sept. 25, 1962 wherein the conductor which was used to wind the coil had a plurality of indentations. When the unit was wound the indentations would align forming passages through which coolant could be forced thereby facilitating the removal of excess heat.
One particular troublesome area is current transformers. Current transformers have no primary of their own but are installed around a cable, a conductor, or a bushing which provides its own insulation from the core and secondary winding. They are used, in one particular application, as part of the instrumentation package of a generator facility. Until the recent development of large turbine generators with current ratings over 34,000 amps, it had been acceptable to design current transformer cases that are cooled by natural air convection. Large transformers were cooled by adding fins to the outer diameter of the case to provide as much area as possible exposed to natural air convection. The primary heat generated in the transformer case is a result of induced circulating currents in the case due to the flux created by the line current.
While most current transformer cases have been constructed of aluminum, for large ratings it has been necessary to build some of copper to reduce the generated heat loss, if the case is air cooled. However, for the newer machines which sometimes have ratings over 34,000 amps, none of the prior art air-cooled cases are desirable.